The animals have remained in Sevastopol’s Cossack Bay aquarium, with Russia saying that it was planning on purchasing new equipment to enhance their operational effectiveness. The dolphins are trained to identify underwater obstacles, locate missing kit, and fight and even kill enemy frogmen.

They are a unique asset – the only other navy to maintain a dolphin force is the US navy, which trains marine mammals including sea lions at a facility in San Diego. Unlike the Soviet dolphins, their American counterparts are – at least officially – never used for combat.

And Dmitry Yunusov, first deputy head of the Henichesk Regional State Administration, just across the straits from Crimea,said they want them back.

"The military dolphins need to be returned to our country in the same way that Russia returned Ukraine’s seized military equipment," he said.

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And he claimed that a new dolphinarium has been built to house the mammals, with a large pool and "very comfortable and civilised living conditions."

The marine mammal training program in Sevastopol’s Cossack Bay has trained dolphins and other sea creatures for navy work since 1965.

Legend has it they were also trained to attach limpet mines to enemy vessels or even carry out “kamikaze” attacks against enemy submarines – using their natural sonar to distinguish enemy from Soviet submarines by their engine noise.

But like may Soviet servicemen, the dolphins fell on hard times with the end of the Cold War.

At the time of the dissolution of the USSR, more than 150 bottlenose dolphins and beluga whales and almost 50 sea lions served in special Navy units.

In 1995, after the collapse of the Soviet Union, the dolphins in Sevastopol came under the control of Ukraine. In 2000, the remaining 27 animals and special equipment were sold to Iran.

Ukraine relaunched the military program in 2012, and the current generation of dolphins at the centre were said to be already proficient at marking lost weapons and underwater obstacles with buoys.